Multiple vehicle subsystems, such as the vehicle brakes, may utilize vacuum as an actuation force. The vacuum is typically supplied by the engine through a connection to the intake manifold, which is at sub-barometric pressure when the throttle is partially closed and regulating the airflow into the engine. However, the engine intake manifold vacuum may not be sufficient for all of the subsystems at all operating conditions. For example, during a catalyst heating mode immediately after engine starting, a high level of spark retard may be used to generate exhaust heat directed to the catalyst, resulting in insufficient vacuum from the intake manifold. In some examples, engine-driven or electrically-driven vacuum pumps may be used to supplement intake manifold vacuum during such operating conditions. However, engine-driven vacuum pumps may disadvantageously reduce fuel economy, while electrically-driven vacuum pumps may lack durability while being expensive, heavy, and noisy.
The inventors have recognized the issues with these options for vacuum generation during operating conditions where engine intake manifold is insufficient, and offer systems and methods to at least partly address them which provide the further advantage of expediting catalyst warming. In one embodiment, a method for an engine includes adjusting a position of an exhaust backpressure valve (EBV) downstream of a catalyst in an exhaust passage based on engine operating conditions and stored vacuum, and flowing exhaust through an ejector arranged in parallel with the EBV in an amount depending on EBV position. The inventors have recognized that the arrangement of an ejector in parallel with a post-catalyst EBV, such as in the various examples described herein, enables both vacuum generation and catalyst heating via closure of the EBV. For example, the EBV may be fully closed to direct substantially all exhaust through the ejector to maximize vacuum generation while expediting catalyst heating via the increase in backpressure at the catalyst resulting from the EBV closure. Alternatively, the EBV may be partially closed to direct a lesser amount of exhaust through the ejector to generate vacuum and expedite catalyst heating during conditions where full closure of the EBV is unnecessary or impractical, such as unstable combustion conditions. Further, EBV control may be tailored for engine operation phases such as cold start, gasoline particulate filter regeneration, normal operation, and shutdown to maximize the benefits of the EBV while reducing negative effects on engine operation by strategically timing and adjusting EBV closure and/or controlling other parameters such as intake throttle position and spark timing to compensate for the effects of EBV adjustment.
The present disclosure may offer several advantages. For example, rapid catalyst heating may be attained. By rapidly heating the catalyst, exhaust emissions during engine cold starts may be reduced. Additionally, vacuum may be generated in copious amounts during the very condition (catalyst heating) when it is less available via the intake manifold. This is accomplished by directing exhaust through the ejector arranged in parallel with the EBV, thus reducing the need for engine-driven or electrically-driven vacuum pumps to supplement intake manifold vacuum.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.